This disclosure relates to a steel composition and an article prepared there from, and uses of the article prepared from the steel composition.
With the present emphasis on alternative power sources, use of wind power for generating electricity is spreading to far flung areas of the globe. Towers for electricity-generating windmills, also referred to as wind towers, are being erected in geographical areas having varied climate conditions, and as such may be subject to mechanical stresses that can arise depending upon these conditions. Operating conditions of greatest concern for wind towers include extreme wind conditions, and extremely cold temperatures.
A wind tower is typically constructed of a generating unit having a wind driven turbine connected to a generator housed in a nacelle, and a tower of an appropriate height and anchored to a base, to support the nacelle. The tower is typically hollow to allow access to the nacelle by a ladder. The height of the tower may be determined according various considerations such as the terrain; the size of the turbine and generating unit; and other conditions such as the average wind speed. The towers are fabricated using materials of construction selected according to the operating conditions for the tower in its site. The tower itself is constructed in several sections joined together by a combination of welding and bolting. Wind towers typically have an expected operating lifetime of about 20 years.
Steel components used in the construction of the primary stress points must withstand the applied stresses under the operating conditions of the wind tower in the environment in which it is situated, for the lifetime of the tower. Wind towers situated at higher latitudes (greater than about 40 degrees north latitude and/or at higher elevations of greater than about 500 meters above sea level) may be subject to a combination of greater extremes of temperature and wind forces than typically encountered at latitudes below these. A combination of conditions which includes low temperatures (as low as −30° C.) and wind speed as high as about 100 miles per hour (mph; about 167 kilometers per hour (kph), sometimes referred as “cold weather extreme” (CWE) conditions, can place significant stress upon mechanical joints of a wind tower. In particular, where a wind tower is constructed of several sections bolted together, a great deal of mechanical stress is carried by the flanges welded to the ends of the section, that provide surfaces for bolting the sections together. A flange that is designed to operate under less rigorous extremes of conditions (e.g., higher minimum temperatures and/or lower maximum wind speeds) may prematurely develop stress related defects in the joints and may have a higher likelihood of failure. The material of construction of the flange (i.e., the steel used) desirably exceeds mechanical requirements appropriate for CWE conditions. Current materials of construction may not consistently provide the desired mechanical performance.
What is needed therefore, is a flange comprising a steel composition that can consistently meet or exceed the mechanical requirements for steels having the properties disclosed in European Norm (EN) 10 113-2:1993. A flange will desirably have low temperature performance suitable to provide defect-free operation over the lifetime of the wind tower.